Annealing of mixed metal oxide electrodes to reduce polarization resistance

Abstract

The thermal treatment of transition metal oxide electrodes such as silver vanadium oxide cathode plates, contacted to titanium current collectors for the purpose of reducing polarization resistance in an alkali metal electrochemical cell, is described. The electrodes are exposed to an elevated temperature of at least about 225° C. for about 8 hours prior to cell fabrication. The present heat treatment regime is particularly useful in cathodes intended for fabrication into a cell powering an implantable medical device with improved polarization resistance as well as reduced heat dissipation.

What is claimed is:  
     
       1. An electrochemical cell comprising anode and cathode electrodes and an activating electrolyte, the improvement comprising; 
       the cell having a lithium-containing anode and a cathode, wherein the cathode contains an active material as a reaction product of at least a vanadium oxide salt and a salt of silver, the anode and the cathode exhibiting reduced polarization after having been contacted by the electrolyte, the reduced polarization being the result of the cathode comprising the active material contacted to a conductive current collector and thereafter heat treated at an elevated temperature prior to cell fabrication so that the cell is dischargeable with the cathode exhibiting a resistivity of less than about 0.2 Ωcm.  
     
     
       2. The electrochemical cell of claim  1  wherein the elevated temperature is at least about 225° C. for at least about 8 hours. 
     
     
       3. The electrochemical cell of claim  1  wherein the cathode is characterized as having been heat treated at the elevated temperature ranging from about 225° C. to about 300° C. 
     
     
       4. The electrochemical cell of claim  1  wherein the cathode is characterized as having been heat treated at the elevated temperature for a heating time of about 8 hours to about 16 hours. 
     
     
       5. The electrochemical cell of claim  1  wherein the electrolyte has dissolved therein a lithium salt. 
     
     
       6. An electrode, which comprises: 
       a) an active material comprising a reaction product of at least a vanadium oxide and a salt of silver; and  
       b) a conductive current collector contacted with the active material to provide the electrode, wherein the electrode is characterized as having been heat treated at an elevated temperature of at least about 225° C. for at least about 8 hours to provide the electrode having a resistivity of less than about 0.2 Ωcm.  
     
     
       7. The electrode of claim  6  wherein the electrode is characterized as having been heat treated at the elevated temperature ranging from about 225° C. to about 300° C. 
     
     
       8. The electrode of claim  6  wherein the electrode is characterized as having been heat treated at the elevated temperature for a heating time of about 8 hours to about 16 hours. 
     
     
       9. The electrode of claim  6  wherein the current collector is selected from the group consisting of titanium, stainless steel, nickel, molybdenum, tantalum, niobium, cobalt, tungsten, platinum, palladium, gold, silver, copper, chromium, vanadium, aluminum, zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. 
     
     
       10. The electrode of claim  6  wherein the active material is selected from the group consisting of silver vanadium oxide, copper silver vanadium oxide, and mixtures thereof. 
     
     
       11. A method for constructing an electrochemical cell comprising the steps of: 
       a) providing an anode;  
       b) providing a cathode of an active material contacted to a conductive current collector, wherein the active material a reaction product of at least a vanadium salt and a salt of silver;  
       c) heating the cathode to a temperature of at least about 225° C. to reduce resistivity of the cathode to less than about 0.2 Ωcm; and  
       d) activating the anode and cathode with an electrolyte.  
     
     
       12. The method of claim  11  including heating the cathode to at least about 225° C. for at least about 8 hours. 
     
     
       13. The method of claim  11  including heating the cathode from about 225° C. to about 300° C. 
     
     
       14. The method of claim  11  including heating the cathode for a heating time of about 8 hours to about 16 hours. 
     
     
       15. The method of claim  11  including selecting the active material from the group consisting of silver vanadium oxide, copper silver vanadium oxide, and mixtures thereof. 
     
     
       16. The method of claim  11  including selecting the current collector from the group consisting of titanium, stainless steel, nickel, molybdenum, tantalum, niobium, cobalt, tungsten, platinum, palladium, gold, silver, copper, chromium, vanadium, aluminum, zirconium, hafnium, zinc, iron, and mixtures and alloys thereof. 
     
     
       17. The method of claim  11  including providing the cathode comprised of silver vanadium oxide contacted to a titanium current collector and then heating the cathode at an elevated temperature ranging from about 225° C. to about 250° C. for a time of about 8 hours to about 16 hours. 
     
     
       18. The method of claim  11  including mixing the active material with a binder material prior to contact with the current collector, wherein the binder is selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, polyethylenetetrafluoroethylene, polyamides, polyimides, and mixtures thereof. 
     
     
       19. The method of claim  11  including mixing the active material with a conductive additive prior to contact with the current collector, wherein the conductive additive is selected from the group consisting of carbon, graphite powder, acetylene black, titanium powder, aluminum powder, nickel powder, stainless steel powder, and mixtures thereof. 
     
     
       20. A method for constructing an electrochemical cell, comprising the steps of: 
       a) providing an anode;  
       b) providing a cathode of an active material contacting a conductive current collector, wherein the active material is a reaction product of at least a vanadium salt and a salt of silver;  
       c) heating the cathode to a temperature ranging from about 225° C. to about 300° C. to reduce resistivity of the cathode to less than about 0.2 Ωcm; and  
       d) activating the anode and cathode with an electrolyte.  
     
     
       21. A method for constructing an electrochemical cell, comprising the steps of: 
       a) providing an anode;  
       b) providing a cathode of an active material contacting a conductive current collector, wherein the active material is a reaction product of at least a vanadium salt and a salt of silver;  
       c) hearing the cathode for about 8 hours to about 16 hours to reduce resistivity of the cathode to less than about 0.2 Ωcm; and  
       d) activating the anode and cathode with an electrolyte.  
     
     
       22. A method for constructing an electrochemical cell, comprising the steps of: 
       a) providing an anode;  
       b) providing a cathode of silver vanadium oxide contacted to a titanium current collector;  
       c) heating the cathode to a temperature ranging from about 225° C. to about 250° C. for about 8 hours to about 16 hours to reduce resistivity of the cathode to less than about 0.2 Ωcm; and  
       d) activating the anode and cathode with an electrolyte.